This invention relates to a roll forming apparatus and method of the type used to cold form metal from sheet, strip or coiled stock into various cross sectional shapes which are typically essentially uniform. The process of roll forming is also known as contour roll forming or cold roll forming. It differs from other rolling operations in which rolling mills are used to reduce metal thickness. In roll forming operations, the metal stock is bent into a desired shape and the gauge of the stock is not appreciably reduced except in the areas where the material is bent.
Roll forming machines generally comprise a series of pairs of parallel spindles or shafts mounted on roll stands for rotation about spaced, horizontal axes. The shafts of each pair rotate in opposite directions so that forming rolls or dies mounted on the shafts both feed and bend the metal stock as it passes therebetween.
Prior art roll forming machines have included mechanisms for rotatably driving either one or both of each pair of shafts. In most conventional roll forming machines, the lower shaft is held in a permanent position relative to the machine bed and the position of the upper shaft is vertically adjusted relative to the lower shaft by means of screw adjusting mechanisms.
A vertical adjustment of at least one of the shafts is necessary to allow for adjustment of the clearance between mated pairs of forming rolls or dies so that the metal can pass therebetween and be formed thereby. Also, the base diameters of successive pairs of rolls or dies normally progressively increase so as to constantly place the metal stock under tension. Accordingly, the separation of the pairs of shafts at the beginning end of a roll forming machine is usually less than the separation of the pairs at the finish end.
Vertical adjustment of the rolls is also required because the pressure to be applied by one pair of rolls may be different from the pressure to be applied by other pairs of rolls because of differences in the forming operations that take place as the stock passes through the successive pairs of rolls. Because of the importance and criticality of this adjustment, the roll stands usually have a scale and pointer arrangement so that the specific location of the upper shaft can be noted for future reference. However, such arrangements are not reliable because, as parts become worn, the pointer and scale arrangements do not accurately indicate the positions of the upper shafts.
When a roll forming machine is first set up to produce a given shape, the positions of the upper shafts relative to the lower shafts are adjusted as necessary. The compressive load applied to the metal stock by the screw adjustments depends to a substantial degree upon the experience of the person doing the setup and, in practice, the specific pressure applied is a matter of "feel". Normally several years are required before a setup man has gained the requisite experience to satisfactorily make the screw adjustments. Since roll forming operations require plural pairs of rolls, even an experienced setup man may need a substantial amount of time to set up a particular job. After the shafts are properly set to produce a good part, additional adjustments may be required if the gauge of the metal changes or the physical properties of the metal change. Change in metal thickness is a common problem because of dimensional variations in the thickness of available metal stock, both across the width of the stock and along its length. If the stock becomes too thin, the forming rolls no longer properly mate with the stock with the result that the part will not be properly formed. The same may happen if the metal thickness increases. Also a jam may occur, causing damage to the shafts or to the forming rolls or other damage to the machine. In some cases, the metal thickness itself will be decreased by the forming rolls and, again, the part will be improperly formed.
If the machine is set up to produce a part one day, and then set up for other jobs, and subsequently set up to produce the same part at a later date, the entire setup procedure must be undertaken anew. That is, in typical factory operations, the upper shaft locations for producing a particular shape are not retained for use when the same shape is to be produced at a later date since, as noted above, the shaft locations are not readily reproducible and it is just as easy for the setup man to set the job up all over again.